1. Field of the Invention
The present invention relates to a fixation framework for a ring-shaped permanent magnet which includes a permanent magnet integrated with a supporting member, and applied to a driving mechanism of a linear motor, etc.
2. Description of the Related Art
An example of a conventional Stirling cycle engine employing a fixation framework for a ring-shaped permanent magnet is disclosed in Japanese Patent Unexamined Publication No. 2001-355513. The disclosed Stirling cycle engine has a piston and a displacer sidably inserted into a cylinder provided within a casing, the piston being reciprocated by a driving mechanism. The driving mechanism for reciprocating the piston comprises: a ring-shaped permanent magnet fixed to one end of a short cylindrical-shaped supporting member, the supporting member being connected to a proximal end of the piston; a magnetism introducing member placed opposite around the inner periphery of the permanent magnet with a magnetic gap; and an electromagnetic coil wound around a core, the core being placed opposite around the outer periphery of the permanent magnet with a magnetic gap. When the piston is operated by the driving mechanism so that it travels in the cylinder and comes close to the displacer, a gas which is in a compression chamber provided between the piston and the displacer is compressed and flows into an expansion chamber provided between the distal end of the displacer and the distal portion of the casing, through a heat dissipating fin, a regenerator and a heat absorbing fin. Accordingly, the displacer is pushed downwardly with a predetermined phase difference relative to the piston. On the other hand, when the piston travels away from the displacer, the inside of the compression chamber is subjected to negative pressure, and the gas in the expansion chamber flows back to the compression chamber through the heat absorbing fin, the regenerator and the heat dissipating fin. Accordingly, the displacer is pressed upwardly with the predetermined phase difference relative to the piston. Throughout these processes, a reversible cycle consisting of two changes: an isothermal change; and an isovolumetric change is carried out, thus a part adjacent to the expansion chamber is brought into a low-temperature state and a part adjacent to the compression chamber is brought into a high-temperature state.
In the driving mechanism of this type included in the Stirling cycle engine generates an alternate magnetic field from the electromagnetic coil when an alternate current is applied thereto. The ring-shaped permanent magnet fixed to the supporting member is reciprocated in the axial direction of the cylinder by the generated alternate magnetic field, while the piston connected to the supporting member fixing the permanent magnet is reciprocated in the cylinder along the axial direction.
Conventionally, the permanent magnet used in such driving mechanism is secured to the cylindrical supporting member by an adhesive. More specifically, as shown in FIG. 3, the permanent magnet M is secured to the supporting member B by an adhesive according to a following method. That is, the permanent magnet M is set to a fixation jig A. An adhesive is then applied to the permanent magnet M, and the supporting member B is set to the fixation jig A so as to contact the permanent magnet M. In this method for fixing the permanent magnet M to the supporting member B while using the fixation jig A, however, a clearance between the outer periphery of the fixation jig A and the inner periphery of the supporting member B as well as that of the permanent magnet M is required in order to remove the supporting member B and the permanent magnet M from the fixation jig A. Moreover, a clearance between the supporting member B and the permanent magnet M as illustrated is required for filling the adhesion when the supporting member B is radially stacked onto the permanent magnet M in order to secure the permanent magnet M to the supporting member B by the adhesive. Because of the clearance of the supporting member B and the permanent magnet M relative to the fixation jig A, or the clearance of the supporting member B and the permanent magnet M, the permanent magnet M may be subjected to decentering relative to the piston connected to the supporting member B. Due to this, a coaxial alignment accuracy of the piston relative to the supporting member B tends to go wrong, thus there is a problem such that it is difficult to accurately keep a precision thereof. Further, in a case where the ring-shaped permanent magnet M expands and contracts in accordance with influences from conditions such as a temperature condition, it may easily break away from the supporting member B due to a thermal expansion coefficient difference thereof. Therefore, it is difficult to stabilize a quality of a product. Still further, applying an adhesive takes labor hours for controlling a hardening process or the like, thus an assembling workability is inferior.